From one aspect, this invention relates to apparatus of the kind comprising a bed of particles and means for feeding into the bed a gaseous fluid and reactant, for example air and a combustible material, in such a manner that, during normal operation of the apparatus, the bed is fluidised and the reactant undergoes a required change in the bed.
In known apparatus of the kind referred to which is used for carrying out combustion, the bed is supported on an upwardly presented face of a horizontal support which is permeable to gases, so that gases can be admitted through the support to fluidise the bed. The maximum rate at which the fluidising gases can be passed into the bed depends upon the size and weight of the particles of which the bed is composed. If the gas velocity is too great, the particles will be blown away from the support and the bed will be depleted. There is thus a maximum rate at which combustible material can be consumed in unit area of this known combustion apparatus of the kind referred to, the limiting rate depending upon the nature of the particles of which the bed is composed. The rate at which combustible material can be consumed may be increased by increasing the area of the bed or increasing the weight of the individual particles. Both of these expedients have attendant disadvantages. A bed of increased size requires larger apparatus which will be more costly and will occupy a greater space. If larger, heavier, particles are employed, the surface area per unit mass of the particles is reduced. In cases where the particles are required to react chemically with the products of combustion, for example to absorb oxides of sulphur, increasing the size of the particles reduces their effectiveness as chemical reactants. Generally, the greater the particle size, the greater the depth of the bed necessary to ensure complete combustion within the bed.
It is an object of the present invention to provide apparatus capable of effecting combustion at a rate greater than can be achieved with known fluidised bed combustion apparatus of the same size having similar particles.